Aligned "no such task" error message with verbose messages.

The message now also starts with "TODO:", like all other messages (except for the usage messages).
Before: 42: No such task.
After:  TODO: No task 42.

tests/t1100-replace.sh

@@ -88,7 +88,7 @@ EOF
 test_todo_session 'replace error' << EOF
 >>> todo.sh replace 10 "hej!"
 === 1
-10: No such task.
+TODO: No task 10.
 EOF
 
 cat /dev/null > todo.txt

tests/t1600-append.sh

@@ -41,7 +41,7 @@ EOF
 test_todo_session 'append error' << EOF
 >>> todo.sh append 10 "hej!"
 === 1
-10: No such task.
+TODO: No task 10.
 EOF
 
 cat > todo.txt <<EOF

tests/t1700-depri.sh

@@ -12,7 +12,7 @@ EOF
 
 test_todo_session 'depriority nonexistant item' <<EOF
 >>> todo.sh depri 42
-42: No such task.
+TODO: No task 42.
 === 1
 EOF
 

tests/t1800-del.sh

@@ -12,11 +12,11 @@ EOF
 
 test_todo_session 'del nonexistant item' <<EOF
 >>> todo.sh -f del 42
-42: No such task.
+TODO: No task 42.
 === 1
 
 >>> todo.sh -f del 42 Roses
-42: No such task.
+TODO: No task 42.
 === 1
 EOF
 
@@ -55,7 +55,7 @@ test_todo_session 'del preserving line numbers' <<EOF
 TODO: 1 deleted.
 
 >>> todo.sh -f del 1
-1: No such task.
+TODO: No task 1.
 === 1
 
 >>> todo.sh add A new task

tests/t9999-testsuite_example.sh

@@ -110,7 +110,7 @@ usage: todo.sh append ITEM# "TEXT TO APPEND"
 TODO: 5 of 5 tasks shown
 
 >>> todo.sh append 10 "hej!"
-10: No such task.
+TODO: No task 10.
 === 1
 
 >>> todo.sh -p list
@@ -123,7 +123,7 @@ TODO: 5 of 5 tasks shown
 TODO: 5 of 5 tasks shown
 
 >>> todo.sh do 10
-10: No such task.
+TODO: No task 10.
 === 1
 
 >>> todo.sh -p list